The present invention relates broadly to switching circuits for use in telephone systems and, more particularly, to routing circuits for routing digital data between a subscriber of a service which requires that data be transmitted between said subscriber's premises and the premises of the vendor of said service.
A number of desirable services could be made available to subscribers if each subscriber's premises could be directly connected to a vendor of each such service. In general these services require the exchange of relatively low speed data between the subscriber's premises and the vendor of the service. These services include intruder detection and control, control of machinery and power monitoring, and automatic notification of emergency services. Such direct connections between the subscriber's premises and a vendor's premises without the need to provide new lines between the two premises are possible using the telephone system.
Digital telephone systems make possible the transfer of data between the central office switch to which each subscriber is connected and the subscriber's premises over the same telephone circuits which are used to transmit and receive voice signals between these two locations. Such a system is described in the copending application described above. In this system, each subscriber's premises are equipped with a remote unit which in addition to providing ordinary voice communications, also provides a number of ports for continually sending and receiving low speed digital data between devices on the subscriber's premises and corresponding devices on a vendor's premises. Data sent over each of these ports is separated at the central office switch by an interface circuit and routed, together with the identity of the sender to a gate circuit which is responsible for communicating the data to the appropriate vendor over a dedicated telephone circuit. Data to be sent to each subscriber's premises from each vendor is collected by the gate circuit and routed to the interface circuit which relays it to the appropriate subscriber's premises. Such a system simulates a permanent circuit between each vendor's premises and the premises of each subscriber of that vendor's service.
The number of subscribers that can be serviced by each vendor over a telephone circuit connecting that vendor to the gate circuit depends on the number of data words being exchanged over the telephone circuit in question. Hence one wishes to minimize unnecessary traffic on this telephone circuit. One problem inherent in simulating a connection between the subscriber's and vendor's premises by continually transferring data words between the two locations is that the volume of traffic on the telephone circuit connecting the vendor to the gate circuit can be quite high, particularly, if that vendor must service a large number of subscribers. In many cases, a large fraction of this traffic is not needed to adequately provide the service in question. For example, in an intruder alarm system, the vendor is only interested in receiving information indicating that one or more alarm circuits has been actuated. Hence, continually sending the status of the alarm circuits in question to the vendor creates unnecessary traffic on the telephone circuit connecting the vendor to the gate circuit. Similarly, when the vendor has nothing to communicate to a particular subscriber, a default data word must still be sent to that subscriber which creates unnecessary traffic on the telephone circuit in question.
It is an object of the present invention to provide an improved gate circuit for routing digital data to and from each of a plurality of vendors over a telephone circuit.
It is a further object of the present invention to provide a gate circuit which minimizes unnecessary traffic on the telephone circuit connecting said gate circuit to a specific vendor of services.
These and other objects of the present invention will be apparent from the following detailed description of the invention and the accompanying drawings.